William Hague has pledged to ramp up support for the Syrian opposition as US secretary of state John Kerry announced £39 million in funding for rebel forces.
After a meeting of international powers in Rome the Foreign Secretary said the UK would increase its assistance, including equipment supplies, to the national coalition.
Mr Hague said Britain would also continue "all our diplomatic efforts", singling out Russia, which has blocked UN action against Bashar Assad's regime.
He said: "We will be continuing our humanitarian assistance. We're already one of the countries that gives the most humanitarian assistance to help refugees and, as far as we can, to help people inside Syria.
"We will be continuing all our diplomatic efforts, including meetings with my Russian colleagues over the next two weeks, including in London; we will be continuing our support for the UN envoy, Mr (Lakhdar) Brahimi, who works painstakingly at this, but we will be doing additional things.
"We will be adding to the assistance, to the equipment that we provide to help the opposition, to help the National Coalition - to help them save lives."
Syrian opposition leaders initially threatened to stay away from the Friends of Syria conference because of what they called "the world's silence" on the atrocities being carried out by Assad's regime but relented after indications fresh aid would be agreed.
Mr Hague and Mr Kerry discussed efforts to renew support for the Syrian opposition during talks in London on Monday.
The US Secretary of State said food and medical supplies would go directly to rebels, through their military council, for the first time in a significant policy shift for Washington. Mr Kerry said Assad "is out of time and must be out of power".
He added: "For more than a year, the United States and our partners have called on Mr Assad to heed the voice of the Syrian people and to halt his war machine. Instead, what we have seen is his brutality increase."